Change code package to org.typelevel.doobie

[jatcwang]

After #1973, we want to avoid having the same package name as the artifact from org.tpolecat %% doobie (otherwise classpath will be a mess if doobie is a transitive dependency)

[armanbilge]

After #1973

Actually technically that's not quite right. The package should change when the artifact coordinates change i.e. org.tpolecat -> org.typelevel, not when the GitHub org hosting the repo changes.